The overall aim of this renewal application is to complete the Hutchinson Study of High School Smoking, a group-randomized trial in adolescent smoking cessation. This randomized trial is motivated by (1) the current unacceptably high smoking prevalence among youth, and its serious public health consequences, (2) the importance of identifying via rigorous intervention trials effective programs for helping youth who smoke to quit, and (3) the considerable potential of telephone counseling using motivational interviewing to be effective with youth. Now nearly two-thirds complete, this ongoing, 2-arm trial includes as participants 2,886 high school seniors (all the smokers and a sample of nonsmokers, identified via their baseline survey responses) from 50 Washington high schools. The adolescent smoking cessation intervention, implemented to participants in experimental high schools during their senior year, is a proactive, individually tailored telephone counseling intervention that incorporates both Motivational Interviewing and cognitive behavioral techniques. Participants are followed to endpoint, approximately 6 months post-high school, to assess the intervention's impact on cessation status, number of quit attempts, change in readiness to quit, and reduction in frequency and level of smoking. Major activities in years 06-07 covered by this application include completion of tracking and outcome data collection, and statistical analyses and reporting of results. It is clear from previous studies that a majority of teen smokers want to quit and try to do so, but with little success. The primary goal of this randomized trial is to develop and evaluate an innovative smoking cessation intervention to help teens succeed in quitting. A positive finding would have significant implications for reducing youth smoking and, ultimately, for improving the nation's health.